Combustion conduit and igniter structure



March 13.2, 1957 s. M. DE CORSO ET AL ,3

COMBUSTION CONDUIT AND IGNITER STRUCTURE Filed June 10, 1954 FIG. i

INVENTORS CLIFFORD E. SEGILEM $.M. DECORSO United States Patent COMBUSTION CONDUIT IGNITER STRUCTURE Serafino De Corso and Clifford E. Seglem, Pittsburgh, Pa., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application June 10, 1954, Serial No. 435,955

1 Claim. (Cl. 60-39.82)

This invention relates to an igniter and more particularly to an igniter for a combustion chamber in which the pressure prior to ignition varies, rendering ignition of thefuel dilficult, and to a method for projecting a flame into such combustion chambers for ignition purposes.

Many combustion chambers operate at a pressure different from atmospheric, usually higher. For example, the combustion chambers of jet engines and gas turbine engines are supplied with air under pressure to secure the high rates of burning necessary to provide the required power. To place this type of power unit in operation, it is customary to first supply air under pressure to the combustion chamber and then ignite the fuel which is injected therein. The pressure within the combustion chamber may vary appreciably prior to and during ignition and the conditions for igniting the fuel therefore vary. 1,3 Torch igniters have been found to be excellent igniters for combustion chambers which operate at a pressure other than atmospheric, but they are subjected to back pressure which is the result of the pressure in the combustion chamber. If the pressure within the combustion chamber varies, so does the back pressure on the igniter, and the fuel and air mixture flowing through the igniter is subjected to changing pressures, flow rates and vaporizing times.

It is an object of this invention to provide a new and improved igniter for combustion chambers in which the pressure varies.

It is another object of this invention to provide a novel and improved igniter for combustion chambers, which igniter is independent of the fluctuations in pressure in the combustion chamber.

A further object of this invention is to provide a novel and improved igniter for combustion chambers, which igniter provides a constant mass flow of air and burning fuel to the combustion chamber regardless of the variations in pressure in the combustion chamber.

A still further object of this invention is to provide a method for projecting a flame into a combustion chamher for the ignition of fuel therein.

Other objects and advantages of the invention will hereinafter become more fully apparent from the following description of the annexed drawings, which illustrate a preferred embodiment, and wherein:

Fig. 1 is a sectional view of the igniter of this invention; and

Fig. 2 is a sectional view of the igniter of this invention taken along line 22 of Fig. 1.

Referring now to the drawings, the reference numeral 12 designates a combustion chamber to which fuel and air are supplied by the nozzle 15, which nozzle is of wellknown construction. An igniter 16 comprising a main housing 31 and a fire tube 34 is secured to the combustion chamber 12 at one end of the fire tube 34 and communicates therewith through an opening 17 in the wall of the combustion chamber 12. The housing 31 has a central bore 32 which is coaxial with the bore 33 of the fire tube 34 and is provided at its upper end with a 43 and is in communication with the venturi section 45 of the passageway 44. Airfrom a source 48 is supplied to air conduit 46 through an air line having a control valve 49 therein.

The main housing 31 is provided with a fitting 51 which supports a heater plug 52 and a heater plug shield 53. The heater plug 52, comprising a resistance wire 54, extends transversely into the bore 32 in the path of the air and the fuel, and the shield 53 substantially surrounds the resistance wire 54 to protect it from. overexposure to the stream of air and fuel in a manner described in more detail and claimed in the copending patent application No. 453,170, filed on August 30, 1954, by Clifford E.

Seglem. A lug 55 on the shield 53 fits onto a keyway 56 in the fitting 51 to ensure proper positioning of the shield 53.

The diameter of the orifice and the pressure of the air supplied through the pipe 46 are so related that the pressure in the bore 42 is at least twice the pressure in the bore 32 to ensure critical fluid flow through the orifice 36. Since the bore 32 is at the same pressure as the combustion chamber 12 because the pressure drop through the fire tube 34 is negligible, the pressure on the input side of the orifice 36 should be at least twice the maximum pressure to be encountered in the combustion chamber 12.

In operation, air under pressure and fuel are supplied to the combustion chamber 12 through the nozzle 15. Air under pressure is supplied to the igniter 16 through the pipe 46 and, as the air flows through the venturi restriction 45, it picks up fuel from the pipe 47 and carries the fuel into the bore 42. The fuel and air flow through the orifice 36 into the bore 32 of the main housing 31 and past the heater plug 52 where the hot resistance wire 54 ignites the fuel. The flame anchors on the shield 53 and, due to the pressure of the air behind it, the flame extends downstream in the bore 32, through the fire tube 34 and into the combustion chamber 12 where it ignites the fuel therein.

The ignition of the fuel in the igniter 16 must be rapid and certain so that a flame quickly extends into the combustion chamber 12 and ignites the fuel therein before the combustion chamber 12 becomes flooded with unburned fuel. A delay in the ignition of the fuel in the combustion chamber 12 results in an excess of unburned fuel which creates an explosion hazard, and, even if no explosion occurs, results in incomplete combustion upon ignition, coating the interior of the combustion chamber and other elements through which the exhaust gases pass with carbon and corrosive compounds. To insure repeated rapid ignition of the fuel in the igniter 16, the flow of air and fuel past the heater plug 52 must be constant regardless of changing conditions of pressure in the combustion chamber 12. If the mass flow of the fuel and air and the ratio of the fuel to the air in the bore 32 is constant, the heater plug 52 is always exposed to the same conditions and the plug 52 can be set and maintained at optimum operating etficiency.

The design and the size of the venturi 45 fixes the fuel-air ratio which does not change even with changes in Patented Mar. 12, 1957 the rate of flow thr ough the venturi 45. If the pressure drop across the orifice 36 is over-critical, there will be non-critical fluid flow through the orifice 36, and the mass flow of the air and the fuel through'the orifice 36 will be independentof pressure fluctuations in the combustion chamber 12 or in the bore 32. Non-critical flow, that flo w which is not affected by pressure variations in the combustion chamber is reached when the pressure on the low pressure side of the orifice 36 is approximately 0-. 53 times thepressure on the high pressure side of the orifice 36. Thus, if the pressure of the air and the fuel in the bore 42 is maintained at a pressure which is "at least twice the maximum pressure to be encountered in the combustion chamber 12, the massfiow, which is the weight of the air and fuel which flows in a unit of time, will'be constant, and since the fuel-air ratio is fixed by the dimensions of the venturi 45 and does not vary, the heater plug 52 is exposed to the same at mosphere each time the combustion chamber 12 is to be lighted, and it may therefore be designed and operated at its maximum efiiciency.

Although the orifice 36 is of comparatively small diameter, it is much larger than'the delicate openings usually present in nozzles for the injection of fuel into a combustionchamber or igniter. The size of the orifice 36 is sufficiently large that it is not prone to clogging as are manyof the smaller passageways in older types of equipment;

Since the fuel is drawn into the vigniter 16 by the flow of air through the venturi 45, the igniter automatically purges itself of fuel each time it is shut off because the fuel flow through the pipe 47 ceases when the pressure of the air in the pipe 46 drops. This eliminates the use of valves'or other controls for the igniter fuel.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claim the invention may be practiced otherwise than as specifically described.

What is claimed is:

In combination, a conduit forming a combustion zone having means for supplying a primary combustible mixture thereto and an igniter comprising a housing providing an elongate passagewa "'having a discharge "end in communication with the combustion zone and an inlet end exteriorly of the combustion zone, means for supplying an independent combustible air-fuel mixture to the housing including a connector providing a bore and having one end secured in the inlet end of the housing and aligning its bore with the elongate passageway of the housing, said bore of the "connector having an outlet of reduced diarneter in direct communicationwiththe said elongate passageway :and an inlet of enlarged diameter, a hollow fitting-providing a venturi section therewithin, said fitting having one end portion received in the enlarged diameter inlet of the connector bore and its other end portion "formed with a passage to admit air in an axial stream to theventurisectiomirid also formed with a passage to admit fuel generally normal to the air passage through the venturi section so that fuel is picked up b'y'the stream and'the'r'e'st'iltan-t fuel-air mixture is directed to'the elongate passageway 'ofthe'housing' "through the reduced diameterennet ofthe'cenneetor, igniter'means disposed in'the passagewayfor ffe'c-ti'ng'cornbustion of the mixture and"producin'g aflam'e"within'the passageway and means within the passageway for holding part of the fianie'andpermit-ting' the remainder of the flameto be forcedthroiigh the outlet-end of the passageway into the combustion-zone by'fl'o'w of the independent combustible mixture.

References -Cited in the. file of this patent UNITED STATES PATENTS 

